This invention relates to apparatus for use in the manufacture of vehicle tires, especially off-the-road (OTR) tires,(including aircraft tires) and to methods for the manufacture of such tires.
In the manufacture of vehicle tires it is common practice to fabricate a tire in steps or "stages". Most usually, the multiple stages employed are carried out on different pieces of apparatus and the product(s) from one stage are transferred to a different stage of operation for further work on the product and/or combination of this product with a further product.
In one example, the manufacture of a vehicle tire includes the step of forming a carcass for the tire on a first piece of apparatus, forming a belt and tread package for the tire on a separate piece of apparatus, and thereafter marrying the belt and tread package to the carcass, commonly employing a further piece of apparatus, to form a "green" tire. In the manufacture of either of the carcass or the belt and tread package, the apparatus includes a cylindrical drum having a rotational axis and an outer cylindrical surface onto which the belt and tread package, for example, is formed. Removal of the formed carcass or belt and tread package from their respective drum requires reduction of the circumference of the drum to release the formed carcass or belt and tread package and provide clearance between the outer circumference of the drum and the inner circumference of the carcass or belt and tread package sufficient to permit removal of the carcass or the belt and tread package from their respective drum. This capability of the drum is most frequently provided for by forming the drum of a shell which includes a plurality of segments, each of which includes a shell member that exhibits an outer arcuate surface. These shells are mounted for radial movement relative to the longitudinal (rotatational) axis of the drum, and when expanded to their radially outward positions, the segments cooperatively define the outer cylindrical working surface of the drum.
In the formation of OTR tires, particularly, it is common to form the green tire on a single drum. In this operation, an inner liner and multiple body plies (bias laid and up to 18 or more plies in an aircraft tire, for example), and one or more belt plies and a tread ply, are laid up on a rotating drum. These tires most frequently include multiple, nonexpansible, usually metallic, bead rings which ultimately form the beads of the tire that mate with the outer rims of the vehicle wheel. This process usually involves the laying down of the inner liner and one or more of the body plies. These plies are wider than the width of the drum so that their opposite side edges project beyond the respective ends of the drum. The process of application and insertion of the multiple bead rings commonly involves the steps of folding the side edges of the plies around their respective ends of the drum, followed by placement of a bead ring adjacent each end of the drum and in engagement with the now radially inwardly extending side edges of the plies. The radial position of the bead ring is chosen to leave about one-half of the side edges of the plies available for folding about the bead ring and radially outwardly of the drum, hence back upon themselves, where the terminal edges of these side edges is married (bonded) to the plies that are overlaid on the drum. This process of laying down one or more body plies, positioning of a bead ring, folding of the plies about the bead ring and back upon themselves, and their bonding to themselves is repeated for each bead ring that is added to the tire. For aircraft tires which may includes eighteen or more body plies, there may be as many as five or six body plies overwrapping each bead ring. It is thus apparent that the inner diameter of the green tire is substantially less than the diameter of the bead rings, so that for a tire which in intended to fit a 20 inch diameter wheel rim, the inner diameter of the green tire on the drum may be as small as 18 inches, for example. Thus, in the manufacture of an OTR tire, there is imposed on the drum a requirement that the drum be collapsible to a greater extent than those drums which are employed in the manufacture of tires having lessor thickness of inner liner, body plies, belt and tread packages, and/or fewer bead rings, etc. In addition to this increased requirement of collapsibility to a relative small diameter, the size and weight of OTR tires imposes a greater strength requirement upon the working elements of the drum as compared to drums for use in the manufacture of lessor sized tires, such as automobile tires. As an additional factor, the relatively great weight of the OTR tires also makes it necessary that the green tire be easily removed from the drum inasmuch as the weight of the OTR green tire does not lend itself to manual manipulation of the tire in an effort to remove it from the drum, as is possible in certain smaller sized (and lighter weight) tires.
Collapsible tire-building drums are well-known in the art. However, in the instance of OTR and similar tires, there is an extensive undercut of the sidewalls relative to the body of the tire. Due to the severity of this undercut it is also necessary that the drum be collapsable longitudinally, i.e., axially, of its length dimension, i.e., in a direction parallel to the longitudinal (rotational) axis of the drum.
In certain prior art, such as disclosed in U.S. Pat. No. 4,445,962, collapse of the drum in the aforedescribed manner requires at least partial dismantlement of the drum so as to provide space internally of the drum into which the circumference-defining segments thereof can be radially collapsed for reducing the diameter of the drum (as opposed to collapse of the drum in a longitudinal (axial) direction) by the necessary relatively high ratio of desired tire outer diameter to the inner diameter of the sidewalls of the tire. Dismantlement, even partial, of the drum increases the cost of manufacture of a tire due to the time involved in dismantlement and reassembly of the drum, and exposes an operator to inordinate danger in the handling of the relatively large and heavy segments of the drum.
One prior art technique suggested in U.S. Pat. No. 4,425,180 for providing for clearance between the ends of the segments and the undercut bead-bearing margins of the green tire has been to design at least alternate ones of the segments with articulated ends and provide for inwardly articulation of the ends simultaneously with the radial movement of the segments. This design suffers from the complicated mechanisms required to effect the articulation, hence inordinate cost of manufacture and maintenance of the drum, and the lack of strength afforded by the articulated ends during such operations as stitching of the sidewalls of a green tire. Further, the presence of the articulated ends of the segments occupies space internally of the drum and limits the extent of permissible reduction in the diameter of the drum.
In U.S. Pat. No. 4,220,494, it is suggested that each segment of the drum be formed from a central section and opposite end sections. Each end section is slidably mounted on the central section to permit axial spacing of the end sections to select different drum widths. The mechanism for effecting this sliding movement includes a splined shaft received in the hollow center of a spiral gear associated with a respective end section. Rotation of the splined shaft effects axial change in the spacing of the end sections, hence change in the width of the drum.
Each central section is connected by links to first and second hubs disposed on a central double-directionally threaded lead screw of the drum such that rotation of the lead screw effects movements of the two hubs in opposite directions along the length of the lead screw. Each of the two end sections of each segment are connected by links to opposite ones of the links which connect the central section to the hub. Rotation of the central lead screw effects axial movement of the hubs and resultant radial movement of the central section. By reason of the linked connection of the end sections to their respective central section, radial movement of the central section further results in sliding movement of the end sections in an axial direction to clear the end sections relative to the undercut bead-bearing margins of the green tire. This mechanism is also subject to excessive costs of manufacture and maintenance as well as potentially inadequate strength to withstand stitching and like operations on the sidewalls of the green tire. Also, this mechanism only provides for equal axial and radial movement of all the segments that go to make up the drum and thereby is limited in the extent of permissible reduction in the diameter of the drum.
It is therefore an object of the present invention to provide a rotatable drum for use in the manufacture of a cylindrical or toroidal product in which the drum is exandable or collapsible both axially and radially of its rotational axis.
It is another object of the present invention to provide a drum which is useful in the manufacture of vehicle tires, particularly off-the-road vehicle tires.
It is another object to provide a method for the manufacture of vehicle tires, particularly off-the-road vehicle tires.